Transpiratory water loss and metabolism of beetles from arid areas in East Africa

Abstract

1. 1. Carabid beetles have rates of transpiratory water loss and metabolic rates which are higher than those of tenebrionid beetles. Within each family, dry habitat beetles have lower rates of water loss than beetles from mesic or hygric habitats, but no habitat-related difference was observed with regard to metabolic rates. 2. 2. When rates of transpiratory water loss of beetles of the two families are plotted as a function of metabolic rates, it appears that for dry habitat beetles, the metabolic rate is the single determinant of transpiratory water loss. 3. 3. This is interpreted as indicating that respiratory water loss is the dominating component of water loss in both carabids and tenebrionids in dry habitats, and that the difference between the families with respect to rates of water loss reflects the difference in metabolic rates. 4. 4. Carabid beetles have considerably higher extracellular concentrations of sodium than the tenebrionids. Seen in the light of the high energetic cost claimed to be involved in sodium transport, this observation is interpreted as indicating that the high rates of water loss and metabolism of the carabids are due to active extrusion of sodium from the cells of the beetles. 5. 5. The ecophysiological significance of these differences is discussed.